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OWNERS MANUAL | Cobolt Modulated DPSS Lasers | D0342-C JUNE 2016
Operating Modes
There are two operating modes: constant power and constant current. The default mode for Cobolt 04 series lasers
when shipped is constant power. In constant power mode the power is monitored on an internal photodiode, and this
is used to regulate the current to maintain a constant power level. In constant current mode the laser runs at a set
current level.
Modulation
Set-up
Without an input signal from the AOM driver to the laser head, there is no laser beam emitted from the laser head.
Both analogue and digital modulation signals has to be applied to the AOM Driver. A typical source for digital and
analogue modulation would be any type of function generator fulfilling the signal levels specified in the table above.
Note that two separate sources are required since the signal levels are different for analogue and digital modulation.
For recommendation on suitable function generators, please contact Cobolt’s technical support. The AOM driver is
set up as follows:
1.
Mount the AOM driver on a suitable heat sink. Make sure that the heat sink can provide adequate heat
dissipation (see specification in section 4.1).
2.
Connect the AOM driver to the Laser Head using the RF cable.
3.
Connect the AOM driver to the source for digital modulation using the digital modulation cable. If you do not
want to modulate digitally, the provided 5V power supply can be used to deliver the necessary digital “on”.
4.
Connect the AOM driver to the source for analogue modulation using the analogue modulation cable.
5.
Connect the DC plug of the 24V power supply to the AOM driver.
6.
Connect the 24V power supply to the mains outlet.
7.
Allow at least 10 minutes warm-up time for the AOM driver for optimum stability.
Modulation Options
The modulation can be digital, analogue or a combination of the two. If no signal is applied on either the digital or the
analogue input, the AOM is in its off-state. The DPSS laser inside the device is however on and it is normal that some
stray light in the μW range can be seen by the human eye when the AOM is in its off-state.
Analogue modulation
In pure analogue modulation, the digital modulation must be in on-state, i.e. a voltage of 3-5V must be applied on the
digital input.
The output power of the laser head has an optimum for a specific voltage of the analogue input. This voltage is device
specific and is stated on the test protocol, but can be easily found by measuring the output power as function of
applied DC voltage on the analogue input. Make sure not to exceed the absolute minimum and maximum voltages
for the analogue input as stated above. The output power as function of the applied analogue voltage is slightly
nonlinear as can be seen in the plot below.
